The Big Bang Theory's Kaley Cuoco has revealed that she and co-star Johnny Galecki secretly dated for two years.

Cuoco, who plays Penny in the sitcom, told CBS Watch! magazine that she and Galecki, who plays on-screen love interest Leonard, split "before the holidays" last year due to the pressure in keeping their relationship out of the public eye.

She said: "It was such a huge part of my life and no-one knew about it. It was a wonderful relationship but we never spoke a word about it and never went anywhere together.

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"We were so protective of ourselves and the show and didn't want anything to ruin that. But that also made it sad, too. That's not the kind of relationship I want - I don't want to be hiding."

The 24-year-old added that she and Galecki are still friends, and were able to stop their break-up from affecting their working relationship.

"When you're dealing with two professionals who have been working since they were both 4 - and who kept their lives extremely private - we didn't want anything other than that," she explained.